You should plan to fly from SUMU (Montevideo) to SAEZ/Ezeiza over a visual corridor via SUCA/Colonia and then SADF (San Fernando).
If I were you I would not try to fly direct from SUMU to SAEZ because it is around 80 NM over the water.
You should also check if there is Customs Service at SADF at the time you are arriving.
SADD/DonTorcuato has been closed to all aircraft operations since 2006.